1. Field of the Invention
The invention relates to transdermal drug delivery, and more particularly to a delivery systems which allows for the variable dosage and/or multiple dosage of medicament in a patient-controllable or pre-set format.
2. Description of the Related Art
Transdermal drug administration has recently come to the forefront as a useful route for continuous dosing of useful drugs. Nicotin patches, for instance, have recently received very broad popular coverage. Medical/pharmacological science is currently testing a wide variety of applications. Many shortcomings and disadvantages of oral or intravenous infusion of medicament are obviated by transdermal application of the drugs.
In general terms, a patch is adhered to a clear area of the skin and the drug is continually absorbed through the skin into the bloodstream for systemic distribution. The skin is particularly useful as it presents large areas for drug administration, as the skin is the largest organ of the body. The utility of such a mode of administration has been demonstrated to those skilled in the art, as described, for example, in my above-noted copending applications.
As the human skin is a very powerful barrier organism, a number of problems must be overcome to enable transdermal drug delivery. Transdermal drug delivery has been demonstrated to be effected by pharmaceutical skin permeation enhancers and electromagnetic stimulation. As described by William R. Good in "Controlled-Release Technology", ACS Symposium Series 348, American Chemical Society, Washington, D.C. 1987, chapters 21-24, the three essentially different approaches may be categorized as physical, chemical and biochemical. The physical category includes iontophoresis, ultrasonic energy and thermal energy, for example.
Iontophoresis, the transfer of drugs through the skin by the introduction of a dc current, was first postulated by S. LeDuc in 1908. At this time however, it has lost favor because of various problems associated with its use. None of the commercially available devices, as far a understood, utilize iontophoresis. The most important problem associated with the technique is its tendency to cause burns under the electrodes. While this is usually due to operator error, burns can occur even with proper technique. Another inconvenience is the messiness of the procedure. Finally, the major drawback to dc iontophoresis is the uncertainty and lack of consistent results.
U.S. Pat. No. 4,592,753 to Panoz describes a transdermal drug delivery device which allows the transdermal application of nitroglycerin. The transdermal or percutaneous delivery is effected by thermal energy released by the nitroglycerin under increased pressure in the drug pouch and during its diffusion into a zone of lower concentration. The wrist band of Panoz provides the pressure on the drug pouch, so that the transdermal delivery is not timed by the device. Also, no accurate control of drug amounts is possible.